It is often that there is a low AC power requirement for a long duration. This could be a remote mountain site radio repeater or WiFi link. These sites generally use less than 50 watts. The requirement is for maybe under 100 watts for at least 24 hours or longer. Most low power, low cost UPS's contain a small gel cell that will provide maybe 15 minutes of power. This may be sufficient for intermittent AC power failures or brownouts. Using an expensive high power UPS with a small load is very inefficient and you will not see a dramatic increase of time the UPS provides power.
The ideal solution is to provide a larger capacity battery connected to the UPS by removing the small internal gel cell and extending the battery wires out to an external deep cycle battery. There are a few caveats. Obviously the size of the external battery could be as large as an automobile battery depending upon your requirements. You will need to run wires out of the small UPS to the external battery. Care should be taken to keep the external battery isolated from any other connections because the battery circuitry could be connected to the hot side of the AC wiring and that could cause injury or become deadly. You may need to provide a supplemental charging circuit because the internal charging circuit won't be able to handle the heavy load of recharging the external battery if it was deeply discharged during a long power outage.
Copyright ©2021 Rick C. Ver 0.13 Oct 24, 2021